24 



Rocks of Noyang. 



Fl 

 Ti0 3 



Si0 2 



Fe o 3 



FeO 



MnO 



CaO 



MgO 



K o 



Na,0 



No. 

 Per cent. 



'66 

 1-05* 



38-66f 

 19-00 



6-37 



9-96 

 -66 



1-52 

 10-61 , 



8-58 



1-08 



1-85 



1. — Iron-Magnesia Mica. 



Molecular 

 Proportions. 

 •35 



Fl + 



SiO. 



Ratio. 



12-76 



4-48 



8-84 



4-23 



,. 2- 

 ,. 1 



,. 1- 



100-00 



The bases in this 

 proportions : — 



1. 



mica are therefore in the following 



EO 

 2. 



E 2 

 1. 



that is, it belongs to a group which Professor Kammelsberg j 

 classes as the third, including, among other micas, lepidome- 

 lane and the haughtonite of Dr. Heddle. § Professor Heddle 

 describes the mica to which he has given the name of 

 haughtonite as occupying a position between biotite and 

 lepidomelane, and he gives the oxygen ratio of the three 

 species as follows : — 



Biotite. Haughtonite. Lepidomelane. 



Si0 o 

 R„0 



21 



19- 



... 



20- 



10- 



... 



15-5 



12-5 



. .. 



7- 



(E0R 2 0) 15- 

 The oxygen ratio of the Noyang mica is — 



Si0 2 ... ' 19-35 



Ro0 3 ... 11-25 



(R0R 2 0) ... 11-36 



The relative proportions in which the silica and the 

 sesquioxide and protoxide bases occur in the Noyang mica 



"* Ti0 2 is calculated out as sphene, which occurs with this mica. 



+ SiO 2 is estimated from the difference. 



I " Uebsr die chemische Zusammensetzung der Glimmer." C. Eammels- 

 berg, N.J.M., 1881, p. 365. 



§ " On Haughtonite — a New Mica," by Professor Heddle. Mineralogical 

 Magazine, Vol. HI., Part XHL, p. 72. 



